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+package com.sf.day02;
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+
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+import java.util.Scanner;
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+
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+public class Test1 {
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+ public static final String IP_ADDRESS = "47.96.190.116";
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+
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+ public static void main(String[] args) {
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+ //常量
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+ String studentName = "zs";
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+ int num = 1;
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+ num = 2;
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+// System.out.println(num);
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+
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+ /**
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+ * 变量的分类(数据类型) :
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+ * 基本数据类型:
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+ * 整型 int
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+ * byte short int long
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+ * 作用:根据字节不同 在内存中所占有的空间不同
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+ * 字节 1 2 4 8
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+ * 计算机的最小单元是位 bit 1字节 = 8位
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+ * -128-127 .....
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+ *
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+ * 浮点型 float double 小数 默认 double
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+ * 4 8
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+ * 单精度 双精度 区别 有效位的权威性
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+ *
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+ * 字符 char '2' 通常
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+ * char a = ’A‘;
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+ * 字符和整型之间的运算 ’A‘+3
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+ * ASCII A = 65 A-Z a = 97 a-z 以此类推 +1
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+ *
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+ * 布尔 boolean 真假 非真即假 true false
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+ * boolean aa = true/false; 条件判断语句
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+ *
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+ * 引用数据类型:
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+ * 三种:类 接口 数组 (String)
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+ *
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+ *
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+ * 变量的分类 (按声明的位置分)
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+ * 类内(方法外) 方法内
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+ *
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+ * 实例变量 (不用static修饰的变量) 类变量(静态变量) static
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+ *
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+ * 声明 初始化 显示初始化
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+ * int a ; int a = 1;
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+ * a = 1;
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+ *
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+ * 包装类: byte short int long
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+ * int Integer byte Byte short Short long Long
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+ * char Character
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+ *
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+ * 基本数据类型 和 包装类 区别 装箱 -- 拆箱
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+ * int a = 0: integer -- null
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+ */
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+
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+ int aaa = 10;
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+ Integer bbb = 10; //ctrl + 鼠标左键
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+ char aa = 'a';
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+ int bb = aa+3; // bb = 68 D 'A' = 65 a = 97
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+ System.out.println( bb);
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+ byte a = (byte) 1000;
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+ short b = 1000;
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+ int c = 10000;
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+ long d =100000L; //l/L
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+// System.out.println(a);
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+ float e = 10.10F; //F/f
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+ double f = 10.10D; //D/d (可选)
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+ float g = (float) 10.10;
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+ short s = 3; //初始化
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+ s= (short) (s+2);
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+ s+=2; //s =s+2;
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+
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+ /**
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+ * 键盘输入
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+ * if语句
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+ * if(){
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+ *
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+ * }else if(){
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+ *
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+ * }
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+ */
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+ Scanner scanner = new Scanner(System.in);
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+// String next = scanner.next();
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+// System.out.println(next);
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+// int nextInt = scanner.nextInt();
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+// System.out.println(nextInt);
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+// boolean b1 = scanner.nextBoolean();
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+// System.out.println(b1);
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+ char c1 = scanner.next().charAt(1);
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+ System.out.println(c1);
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+
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+ /**
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+ * 随机数
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+ */
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+ double random = Math.random(); //[0,1)
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+ //INT [0,99]
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+ int random1 = (int) Math.random();
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+ }
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+
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+ @org.junit.Test
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+ public void t1(){
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+ System.out.println("--");
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+ }
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+}
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